// Physical memory allocator, intended to allocate
// memory for user processes, kernel stacks, page table pages,
// and pipe buffers. Allocates 4096-byte pages.

#include "types.h"
#include "defs.h"
#include "param.h"
#include "mmu.h"
#include "spinlock.h"
#include "swapper.h"

struct run {
  struct run *next;
};

struct {
  struct spinlock lock;
  struct run *freelist;
  int allocated_pages; //keep the total number of allocated pages
} kmem;

// Initialize free list of physical pages.
void
kinit(void)
{
  extern char end[];

  initlock(&kmem.lock, "kmem");
  char *p = (char*)PGROUNDUP((uint)end);
  for( ; p + PGSIZE - 1 < (char*) PHYSTOP; p += PGSIZE)
    kfree(p);
  kmem.allocated_pages = 0; //init to 0
}

// Free the page of physical memory pointed at by v,
// which normally should have been returned by a
// call to kalloc().  (The exception is when
// initializing the allocator; see kinit above.)
void
kfree(char *v)
{
  struct run *r;

  if(((uint) v) % PGSIZE || (uint)v < 1024*1024 || (uint)v >= PHYSTOP) 
    panic("kfree");

  // Fill with junk to catch dangling refs.
  memset(v, 1, PGSIZE);

  acquire(&kmem.lock);
  r = (struct run *) v;
  r->next = kmem.freelist;
  kmem.freelist = r;
  kmem.allocated_pages--;
  release(&kmem.lock);
}

// Allocate one 4096-byte page of physical memory.
// Returns a pointer that the kernel can use.
// Returns 0 if the memory cannot be allocated.
char*
kalloc()
{
  struct run *r;

  acquire(&kmem.lock);
  r = kmem.freelist;
  if(r) {
    kmem.freelist = r->next;
    kmem.allocated_pages++;
  }
  release(&kmem.lock);
  return (char*) r;
}

int get_free_percent() {
	double total = (double)PHYSTOP;
	double allocated_size = 100. * (double)(kmem.allocated_pages * PGSIZE) / total;
	return 100 - (int)allocated_size;
}

int swapNeeded() {
	int free_percent;

	acquire(&kmem.lock);
	free_percent = get_free_percent();
	release(&kmem.lock);

	if (free_percent <= MEM_T) {
		return 1; //need swap
	} else {
		return 0; //swap not needed
	}
}
